Nasty Little Hydrostatic Transmission Secrets...

MikePA · Mar 1, 2004

I believe you are refering to the main hydraulic pump mounted on the engine that supplies fluid to the 3 point and loader Ect. 
My bad. /forums/images/graemlins/blush.gif /forums/images/graemlins/smile.gif

jinman · Mar 1, 2004

( But it still seems to me that the tractor should be able to back itself out of a hole, carry its own weight so to speak. Twice I have been buried where I couldn't get the wheels to spin. )

Brad, when I first heard of this problem, I thought about your having a full FEL bucket while trying to back up the slope. I had just about decided that your front wheels under the load were causing the extra traction and keeping you from spinning your rear tires. I was going to suggest that you take your tractor out of 4WD and see if you could spin the rears. Then, you said you could use the bucket to push yourself out and I realized the bucket had to be empty to perform this maneuver and could not be putting extra pressure on the front. I am just as baffled as you as to why your tractor can't "snatch" itself up that slope or at least spin the tires.

Yesterday I went out to check some drainage ditches I dug several weeks ago. One had water backed up and I needed to cut the ditch a little deeper in one place. I drove down the bank at 90º to the ditch and with one scoop, I filled the bucket with wet, muddy soil. As I went to back up, the tractor's wheels started spinning and I sat there with 3 of my 4 wheels churning up dirt and mud. I had plenty of power, but my R4s didn't have the traction. Since I was in low-turtle, I shifted to rabbit just to see if the tractor had enough power to spin the wheels there too. It didn't. The relief valve immediately lifted. I shifted back to the lower range, and I had to dump my bucket and then use it to push myself out of the ditch. I guess what you need is a lower gear. /forums/images/graemlins/crazy.gif Do you know the ratio of the final drive in low? You do have three ranges don't you?

Glenn9643 · Mar 1, 2004

Seems to me that a comparison to this is the gearbox on a bush-hog. My 286 has a 110HP rated gearbox, but my 1455v has nowhere near that power, but operates the bush-hog fine. A 110 or higher HP tractor could certainly damage it without using caution.
Provided that the transmissions were set to accomodate the most powerful tractor using it the smaller tractors within the class would get full benefit from the transmission. My opinion is that any transmission on a tractor should put the power on the ground. If the wheels won't spin it should pull the engine down before the transmission gives!

jinman · Mar 1, 2004

( My opinion is that any transmission on a tractor should put the power on the ground. If the wheels won't spin it should pull the engine down before the transmission gives! )

I agree! But it seems that NH has a tractor that is designed just the opposite. It's transmission is meant for the lowest horsepower in a class and the larger hp ratings are protected/limited by the relief valve. That's the frustration. /forums/images/graemlins/frown.gif

PineRidge · Mar 1, 2004

What does this imply for operation, or why should any of us care? Well, this means that if you set up a circumstance where the TC35D will open the relief valve and stall, in the same situation, the TC40D and TC45D will do no better. The transmission physically cannot make use of the additional horsepower and torque of these engines. For pushing and pulling in Low Range-Turtle, the TC35D will have just as much power as its big brothers if the engine doesn't stall.


Jim your comments kept nagging me most of last evening. It quickly settled in that my TC-40D HP and your TC-45D HP will deliver no more HP to the rear wheels than the TC-35D HP. I have to admit that I am not thrilled with this scenario but I am also aware of the fact that there isn't a whole lot that we can do to change a thing.

I am also wondering just as you as to how many other manufacturers have done exactly the same within their product lines.

Even though I have mixed feelings about this whole affair I am still a believer in the HST transmission and it's ease of operation. I for one am not ready at this point to head for the dealership to trade off my HST.

OkeeDon · Mar 1, 2004

Once again I have to ask, doesn't it depend on where the relief valve is set? If the 35 can pop off the valve, then it sounds correct that all of them are equal in pulling/pushing. But, if the 35 runs out of power (horsepower, torque, whatever) before the valve pops, then the 40 and 45 should do better. And, if the 40 runs out of power before the valve pops, the the 45 should do better. Doesn't it depend on where the valve is set?

tc35dforme · Mar 1, 2004

I'm a little confused and a bit suspicious about this theory.

On water pumps, lets say you pick a pump rated for 250 GPM at 50 psi...and the resulting required horsepower based on the pump design is 10 HP. Plug in the pump and you'll get 250 GPM at 50 psi.

Now if you substitute a 7.5 HP motor, the pump will still move water, but it will peak at a lower flow and pressure. The result is that the pump will deliver less work ( power ) with the lower HP.

I have to think the Class III hydros are similar. The transmission has to be capable over handling the maximum horsepower. At the max...the transmission can deliver a certain amount of 'work'. lower the horsepower and the 'work' is lowered.

It would be similar to throttling down. The only change is the power delivered to the transmission and the result is less 'work' capacity.

Maybe we should go to a dealer and chain a TC35D and a TC45D together and have a pull off !! /forums/images/graemlins/grin.gif /forums/images/graemlins/cool.gif

If my logic is off let me know !

slowzuki · Mar 1, 2004

Nope! Think again!

The only thing the larger tractor can't do is xfer more torque to the ground. This only happens in relief conditions. The more hp tractor will pull larger loads or pull faster in non-relief situations. HP and torque are two different things.

Ken

( Jim your comments kept nagging me most of last evening. It quickly settled in that my TC-40D HP and your TC-45D HP will deliver no more HP to the rear wheels than the TC-35D HP. )

Soundguy · Mar 1, 2004

( if the 35 runs out of power (horsepower, torque, whatever) before the valve pops, then the 40 and 45 should do better )

True.. but if the 35 can pop the valve, and not stall the wheels or engine.. it is producin gthe maximum power to the power train.. ( under this theory )..

Glad i have a 12x4 manual gear tranny on my 1920...Me and the clutch and the gears get to decide when the tractor stalls..

Soundguy

JayC · Mar 1, 2004

I don't know much about this sort of thing, but it sure is intriguing! I am curious, though, do you think these HST "limitations" apply to the new TCxxDAs?